Over eighty million intravenous infusions of substantial quantities of liquids containing various nutrients, minerals, drugs or blood are administered to patients each year in the United States. These intravenous (I.V.) infusions typically administer hundreds to thousands of cubic milliliters of liquid from glass or plastic reservoirs, through a conduit of plastic tubing which terminates in a hollow needle that pierces the skin and an underlying blood vessel, into which the liquid is administered.
It is believed that in approximately 15-20% of patients receiving I.V. infusions, blood clots form within the needle, clogging it and terminating the administration of the fluid, minerals, drugs or blood which are needed by the patient. A clogged needle must generally be replaced by an additional needle puncture at a new skin and blood vessel puncture site; though from time-to-time efforts are made to blow the blood clot out of the needle and into the patient's circulation by applying very high pressures to the clogged needle with a liquid-filled syringe. Such efforts, though undertaken to spare the patient the additional pain and tissue damage of added needle puncture, are generally regarded as less-than-optimal medical practice.
The offending clots within the needles that clog them and stop fluid administration consist of elements from the blood that flows in the region of the needle tip. These blood clots can form whenever the flow of fluid through the needle is interrupted for a sufficient period of time. This can occur whenever the supply of liquid within the reservoir is depleted or whenever cold flow of the plastic conduit or changes in the patient's position produce resistance within the conduit or at the needle tip with respect to the blood vessel wall that cannot be overcome by the hydrostatic head of pressure furnished by the practice of hanging the liquid reservoir above the patient.
To overcome such changes in resistance within the conduit and at the needle tip, positive displacement pumps are being employed with increasing frequency for administration of I.V. infusions. However, such pumps commonly introduce the danger that when the supply of liquid in the reservoir has been depleted, continued pumping can rapidly deplete the residual supply of liquid remaining in the conduit and cause air to be pumped into the patient with possible fatal results.